One of the most confounding messages in mainstream nutrition is that eating more than the U.S. RDA of 0.8 g/kg is bad for you. Related to this is the message that animal protein is unhealthy and everyone would be better off swapping out meat for a plant-based diet.

Two new studies show this couldn’t be further from the truth. Published by Nova Southeastern University in Florida, both studies decided to put protein to the test. In the first study, researchers wanted to see what would happen when they put lean, trained individuals on a super high-protein diet. For 8 weeks, subjects ate an average of 307 grams of protein per day (4.4 g/kg /bodyweight), which is the highest amount ever tested in a randomized trial.

Subjects were instructed to simply add protein on top of their regular calorie intake in order to achieve the prescribed 4.4 g/kg intake daily. They didn’t modify their fat or carb intake in order to make room for the extra protein. The additional protein resulted in them consuming an extra 800 calories per day. Much of the extra protein came from whey protein. There was also a control group that was instructed to maintain their current diet, which averaged out to a protein intake of 1.8 g/kg/day.

The study didn't include an exercise intervention, however, subjects had an average of 9 years training experience and were instructed to continue their current workouts.

Results showed that the high-protein group gained 1.9 kg of lean mass and reduced body fat percentage by 0.6 percent. This means that if you’re active, consuming protein in excess of “supposed needs” doesn’t lead to fat gain. Remember that the high protein group was supplementing with protein to the tune of an extra 800 calories a day compared to the control group, which makes the findings particularly noteworthy and pretty well dispels the notion that “a calorie is just a calorie.” That is, protein calories in excess of requirements are not metabolized by the body in a manner similar to carbohydrate, which get stored as body fat.

The surprising results can at least partly be explained by the fact that a large part of the extra protein intake in the high-protein group came from whey protein, which has a particularly high thermic effect, increasing metabolic rate during digestion. Whey contains more of the amino acid leucine than any other protein powder, eliciting a greater increase in protein synthesis.

The same research group then performed a second study to test how a heavy strength training program in conjunction with a very high-protein diet would affect body composition, performance, and health. This time, they had trained men and women perform a well designed periodized training program for 8 weeks during which they either ate their normal diet containing roughly 2 grams of protein per kg of body weight a day or a high-protein diet that bumped protein up to 3.4 g/kg a day. The extra protein was added on top of regular calories and could be gotten from whole food sources or whey or beef protein powder.

The body composition changes were much more favorable than in the previous study, leading researchers to conclude that a high-protein intake can favorably alter body composition as long as changes are also made in one’s exercise training regimen. They called attention to the fact that the high-protein group lost significantly more fat than the normal protein group despite eating about 400 more calories per day.

It’s possible the greater loss of fat mass may be due to the higher protein intake increasing energy expenditure during sleep and daily life. There was surely a thermic effect in the higher protein group such that the amount of calories burned during digestion and assimilation increased more in the 3.4 g/kg group.

Additionally, researchers suggest the high-protein group may have increased their activity levels for a greater daily calorie burn. A previous study found that overfeeding produced an increase in energy expended in physical activity. This is the opposite effect of what happens when people cut calories. When dieting, people tend to decrease physical activity and lower their daily energy expenditure (likely an unconscious effect of the hypothalamus in the brain to prevent weight loss when fuel sources are scarce).

Another possible explanation is that the more advanced training status of the high-protein group could lend itself to greater energy expenditure in daily life.

Both groups gained the same amount of muscle mass, which is likely due to the rigorous training program. It should be noted that the high-protein group had higher compliance with the training and a stronger training background (4.9 training years versus 2.4 in the control group). Of course, it is quite hard for trained people to gain muscle, making the fact that the high-protein group gained the same amount of muscle as the control group a remarkable point.

Based on these incredible results, you’re probably wondering if there are any drawbacks to a very high protein intake. Neither study went into depth regarding possible side effects, however the second 3.4 g/kg trial included a basic metabolic panel of which all markers were normal in both groups. The first 4.4 g/kg study didn’t include a metabolic panel, but a few subjects in that study reported GI distress as well as feeling “hot” during the study.

GI distress is a common effect of a high-protein diet. When protein particles that are incompletely digested reach the gut they cause inflammation. Additionally, high-protein diets tend to lack fiber from plants, which can exacerbate the problem.

It’s unclear why the subjects felt “hot” in response to the high protein intake but it could be due to the high thermic effect of protein or some related mechanism since an increase in metabolic rate often brings with it a higher body temperature.

Take Away Points

#1: If you want to improve body composition by building lean muscle, a high-protein, high-calorie diet in the range of 3 to 3.5 g/kg a day in conjunction with heavy training can help you get fast results.

#2: Distribute protein evenly at meals to sustain muscle building all day long. This is worth mentioning because most people eat the majority of their protein at dinner, skimping on it during the day.

#3: Hardcore training with weights is key if you want to put on lean muscle mass. For conditioning, strongman or intervals should be used. Aerobic exercise should be avoided.

#4: Choose the highest quality, most digestible proteins. If the amino acids in protein aren’t being properly digested, they won’t do you any good. Animal proteins tend to be well digested—just make sure to chew them properly!

#5: Improve GI health by eating vegetables or fruit with every meal. Not only will fruits and veggies provide indigestible fiber for a healthy gut, they will raise blood antioxidant status to eliminate free radicals that cause inflammation.

#6: If you are overweight and your primary goal is fat loss, a high-calorie, high-protein intake probably isn’t indicated. Based on present evidence, it’s recommended that you reduce your carb intake to make room for the extra protein calories instead of piling the protein on top of regular calorie needs.

#8: Based on a previous high-protein study in which sedentary individuals gained muscle eating 1.6 g/kg of protein, researchers recommend that non-exercising subjects who want to optimize lean body mass eat two times the U.S. RDA. Greater lean body mass has the benefit of increasing metabolic rate and insulin receptor sites. It also promotes strength and functionality as well as longevity and better outcome in diseased states.

References

Antonio, J., et al. The effects of consuming a high protein diet (4.4 g/kg/d) on body composition in resistance-trained individuals
. Journal of the International Society of Sports Nutrition. 2014. 11(19).

Antonio, J., et. al. A high protein diet (3.4 g/kg/d) combined
with a heavy resistance training program improves body composition in healthy trained men and women – a follow-up investigation. Journal of the International Society of Sports Nutrition. 2015. 12(39).